1. Field of Invention
The present invention relates to a method of manufacturing a microlens which constitutes, for example, a microlens array plate suited for application to an electrooptic device, such as a liquid crystal device. The invention further relates to a microlens manufactured by the manufacturing method, a microlens array plate, an electrooptic device including the microlens, and an electronic equipment including the electrooptic device.
2. Description of Related Art
In a related art electrooptic device, such as a liquid crystal device, various wiring lines, such as data lines, scanning lines and capacitance lines, and various electronic elements, such as thin film transistors (hereinbelow xe2x80x9cTFTsxe2x80x9d) or thin film diodes (hereinbelow xe2x80x9cTFDsxe2x80x9d), are formed within an image display area. In each pixel, therefore, a region through or from which light capable of actually contributing to display is transmitted or reflected is essentially limited due to the existence of the various wiring lines and electronic elements, etc. Specifically, regarding each pixel, the opening rate of each pixel as is the rate of a region through or from which light actually contributing to display is transmitted or reflected (that is, the aperture region of each pixel), to the whole region, is about 70%, for example. Illumination source light or external light which is entered into the electrooptic device mostly includes parallel light rays, at least, when passing through an electrooptic substance layer, such as a liquid crystal layer, within the electrooptic device. However, in a case where parallel light rays have been entered into the electrooptic device, only that part of the whole quantity of light which is proportional to the opening rate of each pixel can be utilized without any contrivance.
Therefore, in the related art, a microlens array which includes microlenses corresponding to the respective pixels can be formed in an opposite substrate, or a microlens array plate can be stuck on an opposite substrate. Due to such microlenses, light rays which ought to progress toward the non-aperture regions of the respective pixels except the aperture regions thereof without the microlenses are collected in pixel units, so as to be guided into the aperture regions of the respective pixels when they are transmitted through the electrooptic substance layer. As a result, a bright display is realized by utilizing the microlens array in the electrooptic device.
The manufacture of this type of related art microlens is provided as stated below. First, a mask which is provided with a pit at a position corresponding to the center of the microlens to be formed is formed on, for example, a transparent substrate. Subsequently, the transparent substrate is subjected to wet etching through the mask, to thereby excavate a spherical recess which defines the curved surface of the microlens. Thereafter, the mask is removed, and the recess is filled up with a transparent medium of high refractivity. Thus, the microlens is formed in which a hemispherical recess centering around the pit having been first provided in the mask is included as a lens spherical surface. The microlens array can be manufactured by forming a large number of such microlenses in the shape of an array.
In the case of this type of microlens, it is important as basic requirements to enhance a lens efficiency and further to diminish spherical aberration.
According to the related art method of manufacturing the microlens as stated above, however, a non-spherical lens cannot be manufactured, although a spherical lens can be manufactured, comparatively easily.
In this regard, in order to manufacture the non-spherical lens, the related art includes a complicated and high-degree manufacturing method, for example, one in which a non-spherical recess is formed from a separate material on a substrate and is thereafter transferred onto the side of the substrate, or one in which a substrate is subjected to a plurality of different etching steps stage by stage. Such a manufacturing method, however, is basically difficult and increases manufacturing costs as well as reduces an available percentage. Further, there occurs the problem that, as manufacturing steps become complicated and high in degree, controlling the degree of non-sphericalness in the non-spherical lens becomes technically very difficult.
The present invention addresses or solves the above and/or other problems, and provides a method of manufacturing a microlens that is capable of manufacturing the non-spherical microlens comparatively easily. The invention also provides the microlens which is manufactured by the manufacturing method, an electrooptic device which includes the microlens, and an electronic equipment which includes the electrooptic device.
In order to address or solve the above, a method of manufacturing a microlens according to the present invention includes: forming on a substrate a first film an etching rate of which for a predetermined kind of etchant differs from that of the substrate; forming on the first film a mask in which a pit is provided at a position corresponding to a center of the microlens to-be-formed; and performing wet etching through the mask, to thereby excavate in the substrate a non-spherical recess which defines a curved surface of the microlens.
In accordance with the method of manufacturing a microlens according to the present invention, first of all, the substrate, for example, a quartz substrate or a glass substrate is formed thereon with the first film the etching rate of which for the predetermined kind of etchant, for example, one of hydrofluoric acid type differs from that of the substrate. Such a first film is formed by, for example, CVD (Chemical Vapor Deposition) or sputtering. Subsequently, the mask in which the pit is provided at the position corresponding to the center of the microlens to-be-formed is formed on the first film. Such a mask may well be formed in such a way, for example, that a second film is formed on one surface of the first film by CVD, sputtering or the like, whereupon it is patterned by photolithography and etching so as to provide the pit. Alternatively, the mask may well be formed directly on the region of the first film except the pit. Thereafter, the first film and the substrate are wet-etched through such a mask. The etching rates for the etchant employed here differ from each other between the first film and the substrate. Therefore, before the etching penetrates through the first film, a spherical recess is excavated in the part of the first film around the pit, by the wet etching which has no directionality. After the penetration, however, a non-spherical recess is excavated because the degree to which the first film is etched and the degree to which the substrate is etched are different from each other.
Thereafter, the non-spherical microlens can be manufactured comparatively easily by utilizing the curved surface which the non-spherical recess thus excavated defines. By way of example, it is permitted to manufacture the non-spherical micro lens by making the substrate a transparent one and filling up the recess with a transparent medium. Alternatively, it is permitted to manufacture the non-spherical microlens by utilizing the recess as a mold. Further, it is permitted to manufacture the microlens being a biconvex lens, by preparing two substrates, each of which is formed with such a microlens, and then sticking them to each other.
In an aspect of the method of manufacturing a microlens according to the present invention, the first film is higher in the etching rate than the substrate.
In accordance with this aspect, due to the etching, the recess in the shape of a pan whose bottom is shallower than a hemisphere is excavated in the substrate unlike in the first film which is higher in the etching rate than the substrate.
In another aspect of the method of manufacturing a microlens according to the present invention, the substrate is made of a transparent substrate; and the step of putting into the recess a transparent medium which has a refractivity higher than that of the transparent substrate is further provided.
According to this aspect, the transparent medium the refractivity of which is higher than the transparent substrate is put into the recess which is excavated in the substrate made of the transparent substrate, and hence, it is permitted to manufacture the microlens as a non-spherical convex lens on the transparent substrate. On this occasion, the transparent medium is made of a transparent resin or the like, and it may well serve as an adhesive. By way of example, it may well serve as the adhesive in the case of sticking a cover glass onto the transparent substrate.
The transparent substrate can also be made of a quartz, for example. In this case, advantageously the quartz substrate is not destroyed even when exposed to high temperatures in forming the first film. However, in a case where the first film is formed at a low temperature, refractoriness is not required of the transparent substrate. The transparent substrate may be, for example, a glass plate or a plastic or resin plate. No problem occurs as long as the transparent substrate is made of a substance which can be etched by the predetermined kind of etchant together with the first film.
In the case where the recess excavated in the substrate is employed as the mold of the microlens, the substrate need not be transparent.
In another aspect of the method of manufacturing a microlens according to the present invention, the first film is made of a transparent film or an opaque film.
In accordance with this aspect, even when the first film is left intact around the recess after the recess has been excavated by the etching, an optical performance concerning the microlens undergoes almost no, or substantially no, negative influence by constructing the first film out of the transparent film. Further, the vicinity of the edge of the recess as is made of the first film can also be employed as the vicinity of the edge of the non-spherical lens.
However, the first film part left around the recess lies at the edge of the optical path of light which is collected by the microlens, so that even when the first film is formed of a semitransparent film or the opaque film, a bad influence which is exerted on the optical performance concerning the microlens is limited.
In another aspect of the method of manufacturing a microlens according to the present invention, the first film is made of a silicon oxide film or a silicon nitride film.
In accordance with this aspect, the first film which has the etching rate different from that of the substrate can be formed comparatively easily. By way of example, the silicon oxide film whose thickness and quality are stable can be formed on the quartz substrate comparatively easily by CVD or sputtering. Moreover, the first film which is transparent as in the above aspect can be formed of the silicon oxide film.
In another aspect of the method of manufacturing a microlens according to the present invention, the etching rate is controlled by condition setting which concern at least one of a sort of the first film, a method of forming the first film, a condition to form the first film, and a temperature of a heat treatment after the formation of the first film.
In accordance with this aspect, the etching rate is controlled by the condition setting which concerns at least one of the sort of the first film relating to, for example, a substance, a density and a porosity; forming the first film, for example, CVD or sputtering; the temperature to form the first film, for example, one below about 400xc2x0 C. or one of about 400-1000xc2x0 C.; and the temperature of the heat treatment after the formation of the first film. Besides, due to such a control of the etching rate, a curvature or a curvature distribution in a non-spherical surface which the recess to be finally obtained defines can be controlled comparatively easily. The curvature or the curvature distribution in the non-spherical surface which the recess to be finally obtained defines can also be controlled by the thickness of the first film.
In another aspect of the method of manufacturing a microlens according to the present invention, the mask is made of a poly-silicon film, an amorphous silicon film or a hydrofluoric acid-proof film.
In accordance with this aspect, the mask in which the pit is provided at the predetermined position can be formed on the first film made of, for example, the silicon oxide film, comparatively easily by, for example, the CVD or the sputtering.
In another aspect of the method of manufacturing a microlens according to the present invention, a plurality of such microlenses are formed in the shape of an array on the substrate.
In accordance with this aspect, a microlens array is manufactured in which a plurality of non-spherical microlenses as stated above are formed in the shape of the array. Therefore, the microlens array which is well suited for application to, for example, an electrooptic device where pixels are arrayed in the shape of an array or a matrix can be manufactured comparatively easily.
In order to address or solve the above, a microlens according to the present invention is manufactured by the method of manufacturing a microlens according to the present invention as stated above (including the various aspects thereof).
The microlens according to the present invention is manufactured by the method of manufacturing a microlens according to the present invention as stated above, so that it can collect illumination source light, external light, etc. with a slight spherical aberration and at a high efficiency, and it can realize the microlens, and further a microlens array or a microlens array plate, which are easily manufactured, which are comparatively inexpensive and whose qualities are stable.
In a case where the microlens according to the present invention is formed directly on the substrate, it has the structural feature peculiar to the present invention, that the boundary between the first film and the substrate exists in the vicinity of the edge of the lens curved surface being non-spherical and that the curvature of the lens curved surface changes remarkably at the boundary. Alternatively, in a case where the microlens according to the present invention is formed through a mold by the 2P method or the like, it has the structural feature peculiar to the present invention, that the curvature of the lens curved surface changes remarkably at a position which corresponds to the boundary between the first film and the substrate in the vicinity of the edge of the lens curved surface being non-spherical.
A microlens array plate according to the present invention includes a large number of microlenses; a transparent member which has concavities that define bottoms of the microlenses; a film which is formed on the transparent member, and which has pits that are formed in correspondence with the concavities and that define edges of the microlenses; and a cover member which is formed on the film. The sectional shape of each of the microlenses is semi-elliptical.
A microlens array plate according to the present invention should preferably be provided such that a sectional shape in the vicinity of a region featuring an angle of 50-60 degrees, which a tangential line to a lens surface in the film forms with respect to a tangential line to an edge of a lens surface defined by the transparent member, is semielliptical.
A microlens array plate according to the present invention should preferably be provided such that a sectional shape of the lens surface in the film is rectilinear.
In order to address or solve the above, an electrooptic device according to the present invention includes the microlens according to the present invention as stated above; a displaying electrode which opposes the microlens; and a wiring line or an electronic element which is connected to the displaying electrode.
The electrooptic device according to the present invention includes the microlens according to the present invention as stated above, so that it can collect illumination source light, external light, etc. with a slight spherical aberration and at a high efficiency by the non-spherical microlens, and it can realize the electrooptic device which is capable of displaying a bright and vivid image. Such an electrooptic device can be constructed as a liquid crystal device of active matrix drive type or the like electrooptic device in which the wiring lines, such as scanning lines and data lines, and the electronic elements, such as TFTs or TFDs, are connected to the displaying electrodes, such as insular pixel electrodes or stripe-shaped electrodes.
In order to address or solve the above, an electronic equipment according to the present invention includes the electrooptic device according to the present invention as stated above.
The electronic equipment according to the present invention includes the electrooptic device according to the present invention as stated above, so that it can realize various operations, such as those of a projector, a liquid crystal TV receiver, a portable telephone, an electronic notebook, a word processor, a video tape recorder of view finder type or monitor direct view type, a workstation, a video telephone, a POS terminal and a touch panel, for example, which are bright and which have excellent display qualities.
Such operations and other advantages of the present invention will be clarified by exemplary embodiments described below.